1. Field of the Invention
The present invention relates to a linear motion guide unit comprised of an elongated track rail and a slider installed onto the track rail for linear movement relative to the track rail and, more particularly, to a linear motion guide unit with lubricating means to apply lubricant to the track rail as the slider traverses the rail.
2. Description of the Prior Art
The linear motion guide units have been conventionally used incorporated in the parts or components for reciprocating motion in fields as diverse as the industrial robots, semiconductor manufacturing machines, inspection instruments, machine tools or the like to satisfy the demands for higher accuracy, high-speed, miniaturization and so on. The recently remarkable development in mechatronics technology extensively requires linear motion guide units that may meet with needs of maintenance-free, especially, the self-lubrication of long service life on its relatively movable sliding areas, along with miniaturization, higher accuracy and high-speed in operation.
FIGS. 17 to 19 in the accompanying drawings show a prior linear motion guide unit disclosed in, for example, Japanese Patent Laid-Open No. 93952/1999. The prior linear motion guide unit is primarily comprised of a track rail 2 and a carriage or slider 1 riding the track rail 2 astride for sliding movement. The track rail 2 is formed in a substantially rectangular shape in cross section, which are recessed on lengthwise side surfaces 3 thereof to provide raceway grooves 4. The slider 1 may move on the track rail 2 by virtue of rolling elements running through the raceway groove 4. The slider 1 includes a casing 5 recessed so as to fit over the track rail 2 for sliding movement with respect to the track rail 2, and end caps 6 mounted to forward and aft ends of the casing 5, one to each end.
The casing 5 is made with raceway grooves 9 in opposition to the raceway grooves 4 on the track rail 2 to allow rolling elements 7 to run through between the confronting raceway grooves 4 and 9. Retainer bands 18 are provided in the casing 5 so as to embrace the rolling elements 7 to thereby prevent the rolling elements 7 from falling out of the casing 5. Bottom seals 8 are attached to the lower surfaces of the casing 5 and the end caps 6 to close clearances between the track rail 2 and the combined casing 5 and end caps 6. The rolling elements 7 run through load areas of raceways defined between the raceway grooves 4 on the track rail 2 and the raceway grooves 9 in the casing 5, then turnarounds formed in the end caps 6 and return passages 12 formed in parallel with the raceway grooves 9 in the casing 5. It will be thus understood that the rolling elements 7 are allowed to run through recirculating passages, each of which consists of the load area of the raceway defined between the confronting raceway grooves 4 and 9, and non-loaded area 22 composed of the turnarounds and return passages 12. The slider 1 is allowed to move in a sliding manner along the track rail 2 by virtue of the rolling elements 7 that roll through the load areas between the confronting raceway grooves 4 and 9.
Lubricating means 15 are fastened to end faces 16 of the forward and aft end caps 6, one to each end cap, so as to ride the track rail 2 astride. The lubricating means 15 are each comprised of a lubricant-impregnated plate 40 coming in sliding contact with the track rail 2, and a backing cartridge 21 to support the lubricant-impregnated plate 40 therein. Each lubricating means 15 is made in a platy configuration of uniform thickness and recessed in conformity with the cross section of the casing 5 so as to fit over and conform to the track rail 2 for sliding movement. The backing cartridge 21 has the contour substantially resembling a gate as a whole, which is composed of a ceiling section 28, a pair of side sections 29, 29 extending downward from the sidewise opposing ends of the ceiling section 28, and lower sections 30, 30 extending towards each other from the bottom ends of the side sections 29, 29.
Each lubricating means 15 may fit over the track rail 2 with its ceiling section 28 lying in parallel with a top surface 14 of the track rail 2, the side sections 29, 29 depending downwards in parallel with the lengthwise side surfaces 3 of the track rail 2, and its lower sections 30, 30 extending towards the lengthwise side surfaces 3 of the track rail 2. Thus, the backing cartridge 21 holds in place the lubricant-impregnated plate 40 by surrounding around the periphery of the lubricant-impregnated plate 40, except areas facing the track rail 2. The lubricant-impregnated plate 40 is uncovered at its fore-and-aft major surfaces: forward and aft end surfaces facing against the end caps 6 and end seals 17 respectively. Thus, the lubricant-impregnated plate 40 is left exposed at its major end surfaces until covered with its associated end cap 6 and end seal 17 on the slider 1. The backing cartridge 21 conceals the periphery of the lubricant-impregnated plate 40 to seal pores in the porous structure, protecting the lubricant-impregnated plate 40 against contamination, breakage and escape of lubricant.
The backing cartridge 21, although may be made of any one of metals, synthetic resins, synthetic rubbers and so on, is invariably made of any substance that may be much subject to either elastic deformation or plastic deformation restorable later in order to provide an easy to replace or handle the lubricating means 15. Where the lubricant-impregnated plate 40 is fitted in the backing cartridge 21, or only the lubricating means 15 is either mounted to or dismounted from the track rail 2 with all the casing 5, end caps 6 and end seals 17 left on the track rail 25, the backing cartridge 21 that may be easily subject to either plastic or elastic deformation without occurring breakage makes it possible to simply fit the lubricant-impregnated plate 40 into the backing cartridge 21 or mount the lubricating means 15 on the track rail 2.
The lubricating means 15 will be attached to the casing 5 with the backing cartridge 21 being urged against the end faces of the end caps 6 fastened on the forward and aft ends of the casing 5, thence the backing cartridge 21 is reinforced at its four corners 22 where holes 24 are made for fastening bolts 25. The end caps 6 and end seals 17 sandwiching the backing cartridge 21 between them are also made with matching holes 26, 27 for the fastening bolts in alignment with the holes 24 in the backing cartridge 21. Thus, the backing cartridge 21, together with the associated end cap 6 and end seal 17 keeping the backing cartridge 21 between them, is held on the slider 1 with the fastening bolts 25, which are stretched through the holes 26, 24 and 27 in the end cap 6, backing cartridge 21 and end seal 17, and ultimately screwed into holes in the casing 5 of the slider 1. With the backing cartridge 21 made of synthetic resin or synthetic rubber, collars 23 fit in holes 24 in such a manner that the collars 23 mostly sustain the squeezing force applied by the fastening bolts 25, which are inserted through the collars 23 and tightened, to thereby protect the backing cartridge 21 against the deformation or distortion that might otherwise happen due to the compressive force when tightened.
The lubricant-impregnated plate 40, as shown in FIG. 19, is divided into lubricant-impregnated halves 41, 41, which are arranged on opposite sides of the track rail 2 so as to separately come in sliding contact with their associated raceway grooves 4 on the track rail 2. The lubricant-impregnated halves 41, 41, assembled in the backing cartridge 21, are arranged spaced apart from one another with a middle area 33 in the backing cartridge 21. Upon assemblage of the lubricating means 15, the lubricant-impregnated halves 41, 41 are separately accommodated in the backing cartridge 21, which is then fastened to the casing 5 in such a relation that the halves 41, 41 are arranged confronting the track rail 2. The backing cartridge 21 surrounding the lubricant-impregnated halves 41, 41 helps hold steadily them in place. Moreover, the backing cartridge 21 as stated earlier serves to cover the lubricant-impregnated halves 41, 41 against contamination and breakage as well as prevent the escape of lubricant. Each of the lubricant-impregnated halves 41, 41 is allowed to provide only as much volume as needed to lubricate the raceway grooves 4 and, therefore, the lubricant-impregnated plate 40 may be made more compact in size.
The lubricant-impregnated halves 41, 41 are arranged in symmetry on the opposite sides of the track rail 2. Accommodating the lubricant-impregnated plate 40 in the backing cartridge 21, therefore, may be completed by putting merely mass-produced lubricant-impregnated halves 41, 41 of the same pattern in the backing cartridge 21 in such a fashion as to invert any one to the other with respect to the line Axe2x80x94A in FIG. 19. This makes it possible to use any mould of the same pattern to produce the lubricant-impregnated halves 41, 41, resulting in the reduction in manufacturing cost of the lubricating means 45. The backing cartridge 21 is made at the ceiling section 28 thereof with a middle area 33 extending towards a top surface 14 of the track rail 2. Thence, the lubricant-impregnated halves 41, 41, accommodated in the backing cartridge 21, are held in such a relation that they are isolated from each other and confined by the upper section 28 with the middle area 33, side sections 29, 29 and lower sections 30, 30. That is to say, the lubricant-impregnated halves 41, 41 are exposed to their confronting raceway grooves 4 on the track rail 2 at only the areas where none of the sections stated earlier exists.
Windows 31, 32 are provided at the upper section 28 and the side sections 29, 29 of the lubricating means 15 to offer much saving in material for producing the backing cartridge 21 and also to make easy of the access to the lubricant-impregnated plate 40. For example, the windows 31, 32 allow monitoring visually the lubricant-impregnated plate 40. Moreover, after consumption of the lubricant, the lubricant-impregnated plate 40 short of lubricant may be supplied with the lubricant through the windows 31, 32. The lubricant-impregnated halves 41, 41 have raised surfaces 42, 43, each of which has a height about half the depth of the associated window 31, 32 so as to make positive engagement with the windows 31, 32. Engaging the raised surfaces 42, 43 with the windows 31, 32 may be carried out with the elastic deformation of either both or any one of the lubricant-impregnated halves 41, 41 and backing cartridge 21, for example, by sidewise stretching somewhat the backing cartridge 21 or compressing the lubricant-impregnated halves 41, 41. Engagement of the raised surfaces 42, 43 in the windows 31, 32 assures reliable fit of the lubricant-impregnated halves 41, 41 inside the backing cartridge 21, helping keep the lubricant-impregnated halves 41, 41 against falling off from the backing cartridge 21, which might otherwise happen before attaching on the slider 1 or after detaching from the slider 1.
The lubricant-impregnated plate 40 is composed of a sintered resinous component of porous structure including continuous voids therein, which are impregnated with lubricating oil. The sintered resinous component for the lubricant-impregnated plate 40 is fabricated by pressing fine powder of synthetic resins in a mould under high temperature. The lubricant-impregnated plate 40 is provided on the inside periphery thereof with convexities 44, which are raised inwardly so as to come in sliding contact with the raceway grooves 4 on the track rail 2 to continually supply the lubricant or lubricating oil from the lubricant-impregnated plate to the raceway grooves 4. Molded product for the lubricant-impregnated plate 40 is any sintered resinous porous component with open cells, which may be produced by filling a preselected mould with the powdery ultrahigh molecular weight polyethylene resin better in bonding with metals and having the grading of, for example, either fine grain size of 30 xcexcm or coarse grain size of from 250 xcexcm to 300 xcexcm, and then heating the molded resin under high pressure. The sintered resinous component produced as described above for the lubricant-impregnated plate 40 has the porous structure of the porosity of, for example, from 40% to 50%.
The lubricant-impregnated plate 40 is prepared by immersing the sintered porous resinous component with lubricant of turbine oil to fill the voids with the lubricant. Dipping the sintered resinous component into, for example, turbine oil for about 30 minutes may provides the lubricant-impregnated plate 40 that is regulated at percentage of lubricating oil content of 41% by weight and thus at oil content of about 2 cc. Percentage of lubricating oil content may be controlled in accordance with the operating condition of the slider 1. The sintered resinous component for the lubricant-impregnated plate 40 may be easily formed with high accuracy of finishing within, for example, about xc2x10.025 mm. This makes it possible to provide the component that is most suitable for the linear motion guide units incorporated into the precision machines.
In the linear motion guide unit equipped with the lubricating means constructed as stated earlier, lubrication of the raceway grooves on the track rail may be effected with the lubricant that is applied from the lubricant-impregnated plate with no external force pressing the plate against the raceway grooves. This makes it possible to reduce frictional resistance that might otherwise much causes from the sliding movement of the lubricant-impregnated plate relative to the raceway grooves, whereby the lubricant-impregnated plate may be less subject to wear owing to relative sliding movement between the lubricant-impregnated plate and the track rail.
In the prior linear motion guide unit as described above, a pair of lubricant-impregnated halves for the lubricant-impregnated plate fits in the backing cartridge by making engagement with the windows at their upper and side peripheral areas. Nevertheless, the end face formed integrally with the backing cartridge, even when abutted against any one of forward and aft surfaces of the lubricant-impregnated halves, supports the lubricant-impregnated halves at their but any one side of the forward and aft surfaces. In current art, therefore, the lubricant-impregnated halves sometimes are not supported successfully. To cope with this, it will be expected to support the lubricant-impregnated plate at both sides of their forward and aft surfaces, thereby making even less the frictional resistance that occurs between the lubricant-impregnated plate and the associated raceway groove when the slider moves over the track rail, keeping the sliding movement of the lubricant-impregnated plate even smoother and more stable, and eventually making even less the wear of the lubricant-impregnated plate, which might be owing to the sliding movement.
The present invention has for its primary object to overcome the problems as described just above, especially provide a linear motion guide unit in which lubricating means is disposed between an end cap and an end seal, the lubricating means being comprised of a cartridge, a lubricant-impregnated plate accommodated in the cartridge, and a backing plate reinforcing the lubricant-impregnated plate, whereby the lubricating means reduces frictional resistance encountered when a slider moves over a track rail, helping ensure smooth reciprocating movement of the slider relatively of the track rail, and much decreasing deformation, wear and clogging, and so on in the lubricant-impregnated plate.
The present invention is concerned with a linear motion guide unit comprising; a track rail provided lengthwise with first raceway grooves and a slider movable with respect to the track rail; the slider being composed of a casing made with second raceway grooves confronting the first raceway grooves and return passages, rolling elements running through load areas formed between the confronting first and second raceway grooves, end caps fastened to end faces of the casing, one to each end face, and provided therein with turnarounds connecting the load areas and the return passages to form recirculating passages where the rolling elements are allowed to run through in an endless manner, lubricating means arranged on end faces of the end caps, one to each end cap, to lubricate the first raceway grooves formed on the track rail, and end seals disposed over the lubricating means; wherein the lubricating means is comprised of a lubricant-impregnated plate made of a sintered resinous component of porous structure impregnated with lubricant, a backing plate attached to any one of opposing major surfaces of the lubricant-impregnated plate to support the lubricant-impregnated plate, and a cartridge enclosing another exposed major surface and periphery of the lubricant-impregnated plate to accommodating therein the lubricant-impregnated plate.
In accordance with one aspect of the present invention, a linear motion guide unit is disclosed, wherein a lubricant-impregnated plate is reinforced or supported with a backing plate attached to the lubricant-impregnated plate to form a composite plate, which is then assembled with a cartridge in such a manner that the lubricant-impregnated plate in the cartridge is lidded with the backing plate. The lubricant-impregnated plate is held or supported on both the opposite sides thereof with the backing plate and the cartridge, respectively, thus kept against deformation or distortion that might otherwise happen due to any external force. As a result, the lubricant-impregnated plate is not urged excessively against the raceway grooves on the track rail, nor are they spaced apart largely away from the raceway grooves. This makes it possible to continue keeping the lubricant-impregnated plate in substantial contact relation with the raceway grooves to incessantly apply a desired amount of lubricant to the raceway grooves. With the slider moving relatively to the track rail, the sliding movement of the lubricant-impregnated plate over the track rail is made even smoother and more stable, so that the frictional resistance that occurs between the lubricant-impregnated plate and the associated raceway groove decreases and, thus, the lubricant-impregnated plate is less subject to wear, which might be owing to the sliding movement.
In accordance with another aspect of the present invention, a linear motion guide unit is disclosed, wherein the lubricant-impregnated plate includes a major portion contained in the cartridge to store the lubricant therein, and a minor portion formed integrally with the major portion and allowed to come in sliding contact with any associated raceway groove formed on the track rail to apply the lubricant stored in the major portion onto the associated raceway groove. In addition, the cartridge is provided therein with a window to allow the minor portion to protrude out of the cartridge. The lubricant-impregnated plate, although enclosed with the cartridge to be held certainly in precise geometry, has a portion raised from the major potion thereof, which protrude outwardly through the window formed in the cartridge, coming in sliding contact with the raceway grooves on the track rail.
In accordance with another aspect of the present invention, a linear motion guide unit is disclosed, wherein the lubricating means is disposed between the end seal and the end cap, and fastened to the casing together with the end seal and end cap by means of bolts, and wherein fastening stress caused when the bolt is fastened down is sustained by both the backing plate and the cartridge so that the lubricant-impregnated plate is free of the fastening stress. The fastening load due to bolts to clamp together the lubricating means and end seals is sustained directly by only both the backing plate and the cartridge and, therefore, the lubricant-impregnated plate is kept against the deformation or distortion that might otherwise happen owing to the fastening load caused by the bolt.
In accordance with a further aspect of the present invention, a linear motion guide unit is disclosed, wherein the cartridge is provided with a collar in which the bolt fits for fastening, and wherein the collar comes in abutment against the backing plate at an area where the bolt extends for fastening, thereby transmit the fastening stress to the backing plate. Thus, the fastening stress caused when tightening the bolt to assemble the lubricating means to the casing is transmitted through the collar nearby around the bolt so that the lubricant-impregnated plate, as free of the fastening load, is protected effectively against the deformation or distortion.
In accordance with another aspect of the present invention, a linear motion guide unit is disclosed, wherein the backing plate is provided with a piercing claw, and wherein the lubricant-impregnated plate is mounted to the backing plate by piercing the lubricant-impregnated plate with the claw.
In accordance with another aspect of the present invention, a linear motion guide unit is disclosed, wherein the lubricant-impregnated plate is divided into a pair of lubricant-impregnated halves with respect to the track rail. Moreover, the sintered resinous component for the lubricant-impregnated plate is produced by heating finely powdered synthetic resin of ultrahigh molecular weight polymers under pressure in a design mould.
In accordance with a further another aspect of the present invention, a linear motion guide unit is disclosed, wherein the track rail has the raceway grooves on lengthwise-extending, widthwise-opposing side surfaces thereof, and wherein the slider rides the track rail astride for sliding movement relatively to the track rail. As an alternative, the track rail is formed in an U-shape in cross-section, which includes widthwise opposing side-walls provided on lengthwise inward surfaces thereof with the first raceway grooves, and wherein the slider fits between the widthwise opposing side-walls for sliding movement with respect to the track rail.
With the linear motion guide unit of the present invention, the sintered resinous component is simply machined to tolerance of about xc2x10.025 and the lubricant-impregnated plate is mounted with the backing plate at any one of the opposite major surfaces thereof while mounted with the cartridge at another major surface. Thus, the lubricant-impregnated plate is certainly held in place with less possibility of deformation and distortion by virtue of the backing plate and the cartridge. That is to say, the backing plate and the cartridge, in combination, effectively keep the lubricant-impregnated plate against deformation and distortion to continue keeping the high accuracy of a clearance between the confronting lubricant-impregnated plate and the raceway groove.
As a result, the frictional resistance occurring between the slider and the track rail may be significantly reduced so that the slider is allowed to traverse smoothly along the track rail. The lubricant-impregnated plate applies continually lubricant to the raceway grooves, which are thus kept in well lubrication, while the problem of wear is eliminated whereby the lubricant-impregnated plate is kept from getting clogged at areas coming in contact with the raceway grooves. Moreover, the lubricating means of the present invention may be simply mounted on the forward and aft ends of the slider of the current linear motion guide unit incorporated in the machine bed and so on. Thus, the present invention contributes to improvement on the self-lubrication performance of the obsolete linear motion guide units.
Other aspect and features of the present invention will be more apparent to those skilled in the art on consideration of the accompanying drawings and following specification wherein are disclosed preferred embodiments of the invention with the understanding that such variations, modifications and elimination of parts may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.